As is known from vibration mechanics, shafts rotating about an axis are subject to flexural vibration, i.e. vibrate radially with respect to the rotation axis of the shaft, and vibrate most when rotating at critical speed.
To enable shafts to function properly even above critical speeds, damping devices are used to absorb the flexural energy of the shaft when it reaches critical speed.
Damping devices are also designed to maintain acceptable radial displacement of the shaft and so prevent damage, and to stabilize flexural vibration of the shaft.
More specifically, damping devices are known which substantially comprise a fixed supporting body; and a ring defining an annular opening the shaft fits through.
When rotating outside the critical flexural vibration speed range, the shaft fits loosely through the opening.
In other words, the shaft does not contact the ring.
Conversely, flexural vibration of the shaft at critical speed brings the shaft into contact with the ring.
Contact between the shaft and the ring first alters the natural frequency and overall rigidity of the shaft, and eventually results in dissipation of heat caused by sliding friction between the shaft and the damping device ring; which sliding friction opposes rotation and flexural vibration, and alters the dynamics, of the shaft.
As a result of the above two phenomena, the damping device opposes any increase in flexural vibration, and so absorbs the energy associated with displacement of the shaft.
A need is felt within the industry to damp flexural vibration of the shaft at critical shaft rotation speeds, while at the same time minimizing friction between the shaft and the damping device at rotation speed which are different from critical shaft rotation speeds.
A need is also felt to reduce the response time of the damping device.